Drum filter



Dec. 10, 1963 E. KROFF DRUM FILTER Filed Jan. 11, 1960 INVENTOR. EUGENE KROFF ATTORNEYS United States Patent 3,113,926 DRUM FILTER Eugene Kraft, Salt Latte City, Utah, assignor to Peterson Filters and Engineering Company, Salt Lake City, Utah, a corporation oi Utah Filed .ian. 11, 196i), Ser. No. 6,583 8 Claims. (Ql. 210-391) This invention relates to continuous filtering apparatus and more particularly to improvements in apparatus for discharge of filter cake from the filter medium of drum-type filters such as disclosed in United States Patent Nos. 2,812,064 and 2,812,065.

The above referred to patents are directed to apparatus wherein a rotary vacuum drum having a porous surface is at least partially immersed in a pulp to be filtered. An endless cloth of filter medium, having a length in excess of the circumference of the drum, has one part looped over a portion of the drum surface for cake pickup and the remainder is threaded through a discharge station spaced from and adjacent to the drum. The filter cake is discharged from the cloth in the discharge section and the cloth is then cleaned and returned to the drum.

In the devices of the above-referred to patents, discharge of the cake from the filter cloth is achieved by passing the filter cloth over a pipe having a series of holes through which wash water or other fluid under pressure is forced through the cloth. The pipe must be stationary so that the holes remain in one position under the cloth passing therearound. Also, the cloth must be maintained taut during its passage through the discharge section which increases the friction between the cloth and the stationary pipe. Movement of the cloth over the pipe under this friction increases wear on the cloth.

Introducing water or fiuid immediately under the cloth, as taught in the prior art patents, is very advantageous since the jet action of the fluid issuing under pressure from the series of holes is not dissipated by leaking, but is almost totally forced through the cloth. This not only thoroughly back flushes the cloth for maximum cleaning, but tends to lift the cake away from the cloth so that it will fall free without scraping. Reduced wear on the cloth permits the use of thinner, less expensive cloths since they have a satisfactory operational life.

Filters on which such a discharge system may be used are as much as eighteen feet wide, or wider, creating design problems of supporting various members for such long spans. Thus, the pipe carrying the wash fiuid must be sutficiently strong to support the cloth under tension without undue deflection in the middle or" the span. The discharge of cake from the cloth is, furthermore, aided by passage of the cloth and cake over a small diameter roller, due to the great diilerence between the circumference at the inside and outside surfaces of the cake. A large diameter discharge roller is, therefore, undesirable. The smaller diameter of the discharge rollers further complicates the design of such discharge rollers.

According to the invention, I have provided a discharge mechanism for filter apparatus which includes a discharge roller comprising a series of spaced rings freely rotatable on a hollow stationary shaft such that air or sluicing sprays issuing from orifices in the shaft pass through the cloth at effective pressures to lift the filter cake from the cloth. This arrangement presents an eflicient cake discharge, increases cloth life by elimination of frictional wear at discharge, and decreases shut-down time. The use of such a discharge means in association with a resilient, variable weight fluid-filled tension roll, compensating for variations in cloth stretch, further increases eificiency of operation.

Included among the objects and advantages of the present invention is the provision of a cake discharge system for a vacuum drum filter which provides substantially increased filter cloth life. The invention includes a discharge roller assembly over which a filter cloth passes for effective cake removal at reduced friction. The assembly provides a fluid under effective cake discharge pressure substantially along the length of the discharge roller which is substantially uniform from points of minimum to points of maximum deflection of the roller. The roller includes a plurality of spaced apart rings rotatably mounted on a pipe having a series of holes therein for inducing a flow of sluicing fluid between the rings and periodically at an effective pressure to pass through the filter cloth for cake discharge. The rings are loosely mounted for free rotation on the pipe and support the cloth for essentially frictionless movement over the cake discharge roller.

These and other objects and advantages will be readily apparent from a study of the following description and appended drawings, in which:

FIG. 1 is a partial transverse section of an improved apparatus schematically showing the invention;

FIG. 2 is a detailed view, in partial section, of a portion of the discharge arrangement of FIG. 1;

FIG. 3 is an enlarged view of a portion of a discharge roll according to this invention; and

FIG. 4 is an enlarged end view of the discharge roll of FIG. 3.

Referring specifically to the drawings, a vacuum drum filter 12 is mounted for partial submergence in tank 29. This drum is provided with a screen-like surface covering its compartmented periphery, in accord with conventional practices, and has end plates 5 supporting hubs 11 for a hollow shaft it The drum is mounted between uprights 56, and the assembly includes a conventional r0- tary valve and conduits to the compartmented periphery (not shown) for operation. Pulp in the tank 29 is generally indicated by the dashed lines 15.

The filtering medium of the illustration comprises an endless band of cloth 13, which is wider than the axial length of the drum 12 such that the sides of the cloth overhang, or overlap, the end plates 5 of the drum. The cloth is then spread to full width as it passes through the cake discharges. The overlapping portion on the drum is generally indicated by reference numeral 14. In a preferred form, a six ounce cloth may be used, due to the reduced wear, whereas the prior art filtering devices used 17-20 ounce cloth.

The endless cloth 13 is longer than the circumference of the drum and is threaded through the discharge station mounted at the side and axially along the drum surface. The discharger includes a training rod 27 variably positionable in slots 28 of the enclosure wall 41. While a rod has been illustrated, it is obvious that a roller may be used where desired. A discharge roller 3i) is mounted below training rod 27 in the discharge section. The cloth 13 passes from the rod 27 and is then looped around the discharge roller 3% The discharge roller 30 comprises a series of spaced annular rings 5i) rotatably mounted on a hollow shaft 55. The spaced annular rings 50 are mounted so as to straddle holes 51 in the shaft or pipe 55. The relationship of the rings and the shaft upon which they are carried are described in detail below. The cloth after passing the discharge roller is then looped over an upper roller 25, downwardly under a tension roller 23, filled with a fluid 24, and upwardly over roller 26. After leaving the roller 26 it passes back onto the lower surface of the drum 12 for a filtration cycle through the pulp tank 20. A spray assembly 7 is illustrated as positioned above the roller 26 for directing a cleaning spray of fluid along the length a, 1 sees 3 of the cloth as it passes around the roller 25. This washing further conditions and prepares the cloth for the filtration cycle. The cake removed from the discharge roll (in a manner later described) falls into a launder 21 which includes a suitable discharge 22.

As shown'in FIGS. 2-4, the discharge roller 33' is comprised of a series of rings 50 which are preferably made of a plastic or rubber-like material mounted with a loose fit on the shaft 55. These rings are spaced apart by the plurality of lugs 52 and under the influence of the taut cloth they rotate conjointly on stationary hollow shaft 55. The rings are preferably of a synthetic resin or plastic which will present a relatively low rubbing friction on the metal shaft 55. Simplicity of design, economy of manufacture and efficiency of operation is achieved by such rings running directly on the shaft without bearings. When liquid is used to discharge cake from the cloth it also provides lubrication between the rings and the shaft.

In the drawings, the lugs are shown only as spacer means, but it is anticipated that each ring 563 may include a series of holes on the opposite side, spaced to register with lugs on an adjacent ring. Each lug would then be slightly longer than the depth of such registering holes.

This arrangement provides an interlocked ring system which also maintains a uniform spacing between the rings. Without the interlocking system, the lugs may be made essentially the thickness of the radial extent of the rings.

The rings are maintained in a relative position on the shaft so that an opening or orifice 51 is maintained substantially centered between two adjacent rings. Air or a sluicing fluid, such as water, is forced through the orifices under sufficient pressure to pass through the cloth and lift the cake from the cloth. To provide effective cake discharge with a low rate of how of sluicing fluid, the lugs are arranged to provide a continuous progression of small chambers passing the jet orifices 51. Each such chamber is formed by the rings on each side, adjacent lugs on each end, the shaft as the inner surface and the cloth as the exterior surface. Tension on the cloth keeps the major slack of the rings on the side of the shaft opposite the orifices 5i, reducing fluid leak under the rings. The lugs prevent leaking through the ends of the chamber peripherally of the shaft 55. Fluid under pressure in the chamber tends to lift the cloth from the rings blowing cake from the cloth portion resting on rings providing a generally uniform cake discharge across the cloth.

As illustrated in FIG. 4, the lugs are triangular to reduce blocking of the orifices and provide a more uniform spray on the cloth, however, they may be made of any suitable configuration. Also, they are essentially the same width as the radial width of the rings so as to provide a tight chamber. The rings, furthermore, are preferably radially thin to maintain the cloth 13 as close as possible to exterior surface of the shaft 55. Consistent with design practice for long life, the rings should be axially narrow.

In operation, rotation of the drum causes movement of the endless cloth through a filtration cycle including passage through the pulp tank with commensurate formation of a cake thereon, a washing and drying where desired. The cloth with a layer of filter cake passes from the drum across the training rod 27. The training rod is movable into various of the slots 28 to obtain the desired operating configuration. The cloth, after passing the training rod, loops around the outer circumferential surface of the rings fill which on movement of the cloth freely rotate on the hollow shaft 55. As the cloth passes around the shaft, water, or the like is sprayed onto the cloth through a minor are formed by the chambers. This blows or lifts the cake from the cloth. The arrangement is, in general, a series of pockets around the periphery of the hollow shaft, which form the chambers when covered by the cloth. The removed cake falls then into the launder 21 for removal. Since the cloth is held under tension against the rings 54 there is substantially no relative movement or slippage between the cloth and the rings.

After passing the discharge roller 3d, the cloth passes over roller 25, where it may be subjected to a cleaning spray 7, and then substantially vertically downward under the fluid tension tube or roller 23. The fluid tension roll may be fluid tight rubber or, essentially, a tube made of porous material, such as canvas or the like, of sufficient porosity to exude a small tiow of fluid along its length to further ciean the cloth. The primary purpose of the fiuid tension roller 23 is to compensate for creep or stretch of the cloth and maintain uniform tension across the width of the cloth as it passes the discharge roller. Further, by assuring substantially equal tension across the cloth, substantially even pressure is exerted on the outer circumferential surface of the rings, thus assuring a uniform application of spray on the cloth.

In a preferred embodiment of my invention, the fixed pipe 55 may be made of standard pipe of l, 3, 4, etc. inches diameter. The size of the rings is determined by the pipe size, and on a relative scale for a six inch pipe would be about 1 inch wide and a radial thickness of inch. It is preferable to use as small a pipe as possible to aid cake discharge, however, the span, which may be up to eighteen feet or more, requires a pipe of sufficient size to maintain a minimum deflection in the center of the span. A six inch pipe may have a deflection of as much as inch to /2 inch at mid point. However, the distance or gap for the jet action will be uniformly /8 inch (the thickness of the rings) across the entire width or length of the pipe. Also, because of the rela tively narrow axial width of the rings, there will be no binding of the rings on the stationary shaft. In each size of filter system, the rings are made sufiiciently thin so as to provide only a single narrow bearing surface of each ring on the stationary shaft. The discharge station provides a sinuous path for the cloth, and by maintaining the various cloth supporter members horizontally closely positioned, the cloth travel around each support covers a substantial portion of the periphery. By keeping the supports small in diameter, a clean cake discharge is accomplished. The flexible tension roller may be journalled in the end plates so as to ride on the cloth in the tensioning loop. By having it so journalled, it rolls on the cloth with no rubbing friction and its flexibility maintains uniform tension across the width of the cloth.

It is to be understood that it is not desired to be limited to the particular description and apparatus design hereinbefore described, but rather by the scope of the claims set forth hereafter.

I claim:

1. In a continuous vacuum filter having a rotary vacuum drum mounted for partial submergence in a slurry tank, an endless filter cloth of a length in excess of the circumference of the drum mounted on a portion of the drum and threaded through a discharge station at one side of the drum, and having means for maintaining operating tension on said endless cloth, the improvement which comprises a hollow, stationary shaft bendable under operating tension of the cloth and disposed in said discharge station and having a plurality of orifices arranged to pass fluid under pressure through the adjoining filter cloth looped thereover, a plurality of spaced-apart rings mounted on said shaft in straddling relation with said orifices, said rings being substantially uniform and having an internal diameter larger than the external diameter of said shaft so as to be freely rotatable thereon,

said cloth being supported on said rings through a portion of their circumference so as to guide the cloth around the shaft without frictional rubbing on the shaft while discharging the cake therefrom, and said rings being arranged for lateral movement with said shaft during bending deflection thereof so as to maintain a substantially uniform distance between the shaft periphery and the supported surface of said cloth.

2. A device according to claim 1 in which spacer lugs mounted on each ring and abuttin the neighboring ring maintain said rings separated.

3. A device according to claim 1 in which each ring includes a plurality of spacer lugs mounted on and extending from one side of each ring loosely mesh with a plurality of depressions on the opposite side of the adjoining ring.

4. In a continuous vacuum filter having a rotary drum mounted for partial submergence in a slurry tank, an endless filter cloth of a length in excess of the circumference of the drum mounted on a portion of the drum and threaded through a discharge station at one side of the drum, the improvement which comprises cloth tensioning and cake discharge means disposed in said discharge station including a series of supports over which the cloth is mounted so as to provide a sinuous course of movement for the cloth from and to the drum periphery, one support of said series comprising a stationary hollow shaft subject to bending movement and having a series of orifices extending along one side arranged to pass fluid under pressure through the adjacent filter cloth in a cake discharging action, means rotatably mounted on said shaft and rotatable by movement of the cloth around said shaft and cooperatively forming with the filter cloth a series of relatively small chambers on said stationary shaft, said means arranged to support said cloth along the length of said shaft and through a portion of the circumference thereof during cake discharging action, and another support of said series comprising a tensioning member for the cloth disposed between said shaft and a point of cloth return to the drum whereby to maintain operating tension on said cloth during passage through said cake discharge station.

5. In a continuous vacuum drum filter having a rotary vacuum drum mounted for partial submergence in a slurry tank, an endless filter cloth medium of a length greater than the peripheral length of the drum looped over the drum and through a discharge station spaced from the surface of the drum, the improvement which comprises a discharge roller mounted in said discharge station and inclusive of a hollow stationary shaft having a plurality of spaced orifices axially aligned along the shaft, and a plurality of members freely rotatab-ly mounted on the shaft to provide a support surface for the said filter cloth looped thereover, said plurality of members being cooperatively engageable with the said filter cloth looped around a portion of the shaft and said plurality of members so as to form on movement of the cloth and said members a progression of small chambers between the cloth and shaft so as to confine fluid therein as each chamber communicates with one of said orifices and thereby provide fluid under pressure in each said chamher for passage outwardly through the cloth in a cake discharging action.

6. A device according to claim 5 in which said plurality of members include rings loosely mounted on said shaft and spaced apart by a plurality of spacer lugs, said lugs providing axial partitions for said chambers.

7. A device according to claim 5 in which said plurality of members include a series of plastic rings spaced to straddle the orifices, and a series of spacer lugs mounted to space said rings on said shaft and form axial partitions for said chambers.

8. In a continuous vacuum filter having a rotary drum mounted for partial submergence in a slurry tank, a discharge station mounted at one side of the drum and spaced therefrom, an endless filter cloth of a length in excess of the circumference of the drum looped over a portion of the drum and looped in a sinuous path from the discharge station, and having means for maintaining operating tension on said endless cloth, the improvement which comprises a hollow, stationary shaft positioned at said discharge station subject to bending under operation tension of said endless cloth, there being a series of spaced orifices in said shaft axially along one side, means freely rotatably mounted on said shaft, said means being arranged to pass fluid under pressure issuing from the spaced orifices through the covering filter cloth in a cake discharge action, said means providing a supporting surface for the filter cloth around a portion of the circumference of said shaft, said means being bendable without binding its rotation on said shaft during bending of said shaft and providing an essentially uniform thickness through a portion of said shaft even under shaft bending whereby to maintain said cloth at a uniform distance from said shaft in its passage therearound, and said means cooperatively engageable with the filter cloth looped therearound for rotary movement around said shaft on movement of said filter cloth.

References Cited in the file of this patent UNITED STATES PATENTS 1,796,673 Truxell Mar. 17, 1931 2,622,448 Lorig Dec. 23, 1952 2,812,064 Siebenthal Nov. 5, 1957 2,916,145 Kaiser Dec. 8, 1959 

1. IN A CONTINUOUS VACUUM FILTER HAVING A ROTARY VACUUM DRUM MOUNTED FOR PARTIAL SUBMERGENCE IN A SLURRY TANK, AN ENDLESS FILTER CLOTH OF A LENGTH IN EXCESS OF THE CIRCUMFERENCE OF THE DRUM MOUNTED ON A PORTION OF THE DRUM AND THREADED THROUGH A DISCHARGE STATION AT ONE SIDE OF THE DRUM, AND HAVING MEANS FOR MAINTAINING OPERATING TENSION ON SAID ENDLESS CLOTH, THE IMPROVEMENT WHICH COMPRISES A HOLLOW, STATIONARY SHAFT BENDABLE UNDER OPERATING TENSION OF THE CLOTH AND DISPOSED IN SAID DISCHARGE STATION AND HAVING A PLURALITY OF ORIFICES ARRANGED TO PASS FLUID UNDER PRESSURE THROUGH THE ADJOINING FILTER CLOTH LOOPED THEREOVE, A PLURALITY OF SPACED-APART RINGS MOUNTED ON SAID SHAFT IN STRADDLING RELATION WITH SAID ORIFICES, SAID RINGS BEING SUBSTANTIALLY UNIFORM AND HAVING AN INTERNAL DIAMETER LARGER THAN THE EXTERNAL DIAMETER OF SAID SHAFT SO AS TO BE FREELY ROTATABLE THEREON, SAID CLOTH BEING SUPPORTED ON SAID RINGS THROUGH A PORTION OF THEIR CIRCUMFERENCE SO AS TO GUIDE THE CLOTH AROUND THE SHAFT WITHOUT FRICTIONAL RUBBING ON THE SHAFT WHILE DISCHARGING THE CAKE THEREFROM, AND SAID RINGS BEING ARRANGED FOR LATERAL MOVEMENT WITH SAID SHAFT DURING BENDING DEFLECTION THEREOF SO AS TO MAINTAIN A SUBSTANTIALLY UNIFORM DISTANCE BETWEEN THE SHAFT PERIPHERY AND THE SUPPORTED SURFACE OF SAID CLOTH. 